The present invention relates to an optical element, such as a gradient-index rod-lens and a capillary. More particularly, the present invention pertains to an optical element having at least one end surface that is inclined with respect to a central axis of the rod lens or the capillary.
A typical gradient-index rod-lens converts light that is sent from a light source, such as a laser diode and a light emitting diode (LED), to a parallel light or converges light that is received through an optical fiber at a predetermined position- To transmit light from one optical fiber to another, two rod lenses are arranged to contact each other Alternatively, a filter, which has desired optical characteristics, is placed between two rod lenses. The lens length of the rod lens is determined according to the intended purpose of the rod lens. For example, the lens length of the rod lens is set in accordance with the distance between the output end of the optical fiber and the rod lens or the distance between the two rod lenses such that the coupling loss is minimized.
FIG. 6 illustrates conventional rod lenses 60, 61 used in an optical communication module. The rod lens 60 on the left side has an output side end surface 60a, which is inclined with respect to a central axis C1 of the rod lens 60. The rod lens 61 on the right side has an input side end surface 61a, which is inclined with respect to a central axis C2 of the rod lens 61.
An optical fiber 64 is held by a capillary 63 and an optical fiber 66 is held by a capillary 65. A filter 62 is placed between a distal end portion 60b of the rod lens 60 and a distal end portion 61b of the rod lens 61. The rod lens 60 converts light that is emitted from the output end of the optical fiber 64 to a parallel light. The parallel light is transmitted through the filter 62 and enters the rod lens 6l. The rod lens 61 converges the parallel light at the input end of the optical fiber 66. The converged light travels through the optical fiber 66 and is sent to another optical element. The two rod lenses 60, 61 optically couple the two optical fibers 64, 66.
The lens length Z of the rod lens 60 is the length of the central axis C1 between both end surfaces. The lens length Z of the rod lens 61 is the length of the central axis C2 between both end surfaces. The distance L between the two rod lenses 60, 61 is the distance between the output side end surface 60b and the input side end surface 61a along the central axes C1, C2.
The distal end portions 60b, 61b of the conventional rod lenses 60, 61 are sharp and easily damaged. For example, the distal end portions 60b, 61b could get chipped when placing the filter 62 between the distal end portions 60b, 61b, or when the distal end portions 60b, 61b are arranged to contact each other. If the distal end portions 60b, 61b get chipped, the distance L changes. Therefore, the lens length Z, which is optimized in accordance with the distance L before the distal end portions 60b, 61b get chipped, is not optimum. Thus, the optical communication module that uses the rod lenses 60, 61 having chipped distal end portions 60b, 61b has great coupling loss. Accordingly, the optical fibers 64, 66 are not optically coupled in the optimum manner. Also, when inserting the rod lenses 60, 61 into a holder such as a cylindrical sleeve, the sharp distal end portions 60b, 61b could contact the holder and get chipped. In this case, the optical module is defective. Similar problem occurs when the end surface of each capillary 63, 65 is inclined. If the sharp distal end portions of the rod lenses 60, 61 or the capillaries 63, 65 get chipped, the chipped pieces could further increase the coupling loss.
The objective of the present invention is to provide an optical element for an optical communication module that is not easily damaged, improves the defect rate, and reduces the coupling loss
The objective of the present invention is to provide an optical element for an optical communication module that minimizes the coupling loss without performing alignment during the assembly of various types of optical modules.
To achieve the foregoing objective, the present invention provides an optical element. The optical element includes a first end surface and a second end surface. At least one of the first end surface and the second end surface includes an inclined surface, which is inclined by a predetermined angle with respect to a central axis of the optical element, and a distal end surface, which is adjacent to the inclined surface.
The present invention also provides a cylindrical optical element. The cylindrical optical element includes a first end surface, a second end surface, and an outer circumferential surface. The first end surface intersects a central axis of the optical element. The second end surface intersects the central axis. The outer circumferential surface extends along the central axis. At least one of the first end surface and the second end surface includes an inclined surface, which is inclined by a predetermined angle with respect to the central axis of the optical element, and a contact surface, which is adjacent to the inclined surface and is perpendicular to the central axis.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings illustrating by way of example the principles of the invention.